Parents need to know that ipl2 for Kids is a section of the huge Internet Public Library experimental resource, which is created and maintained by professors and students at library and information science programs. The site is organized by subject and does link to other sites. It may be a bit too cluttered for younger students to find what they're looking for on their own, but for older students, parents, and teachers, it's a well-stocked resource. Kids can submit a question (barring medical, legal, tax, and personal opinion) to a volunteer librarian and receive a well-researched answer back within about a week. Source information taken directly from the site.
Internet Public Library - http://www.ipl.org/div/kidspace/
Merriam-Webster's Word Central - http://www.wordcentral.com/home.html
Smithsonian Education - http://www.smithsonianeducation.org/index.html